This invention relates generally to image reconstruction and, specifically, to methods for generating image data based on Electrical Impedance Tomography.
The principles of electrical impedance tomography (EIT) are based on knowledge that media under examination have variations in electrical properties, e.g., conductivities and permittivities, which are highly correlated with material characteristics such as density or chemical composition. For example, in the human body there are significant variations in electrical conductivity among body tissues.
In industrial activities and other non-clinical applications, it is desirable to perform non-invasive monitoring and, sometimes, imaging to determine the composition of a body volume, or to characterize the size and shape of a feature, or other condition within an object of interest. Generally, EIT is useful for imaging features within a volume that are characterized by distinguishable electrical properties. Oftentimes features within volumes having different densities can be resolved on this basis. For example, in multiphase fluid mixtures it is known that conductivities will vary based on phase (e.g., liquid or gas) or chemical composition. In principal, electrical measurements performed with relatively simple instrumentation can provide data indicative of where in the volume a particular material is located, and the relative proportions of different constituents. Examples of mixtures for which phase concentrations can be determined are solid-liquid compositions such as slurries, gas-liquid compositions such as present in oil pipe lines, and, generally, liquid-liquid and solid-gas-liquid mixtures. The mixtures may be stationary or flowing. In the case of fluids flowing through a pipe, conductivity determinations among materials of different phases, or between materials having different chemical properties (e.g., water and oil), can lead to determinations of relative volumes present. In the past, volume fractions of liquid and gas phases in a pipe have been inferred based on electrical impedance measurements. With respect to EIT imaging it is conventional to acquire data by placing a series of electrodes along the periphery of a body under study, e.g., in a circle along an interior surface of a pipe. See U.S. Pat. Nos. 4,486,835; 4,539,640; 4,920,490; and 5,381,333, all of which are incorporated herein by reference. In the measurement systems described by the foregoing literature the measured voltage or current signals are used to reconstruct spatial features within the volume under study so that an image representative of the features can be generated. In this regard, there is what is often referred to as an inverse problem wherein there may not be a unique solution, i.e., image, corresponding to the acquired data. To overcome this it is necessary to impart a relatively large number of sets of excitation patterns to the electrodes. With this data, algorithms are applied to find a conductivity distribution.
When the electrodes are positioned along a plane cutting through the body under study, the algorithms may provide a conductivity distribution along the same plane. Generally, a wide variety of mathematical methods and numerical techniques have been applied to determine a conductivity distribution which resembles that of the body under examination. Extensive computations have been required in order to generate useful image resolutions. It is desired to find techniques by which satisfactory image generation can be had with fewer computations performed in shorter periods of time in order to bring EIT-based image reconstruction to a larger array of commercial applications.